The present invention relates to a process for the dimerization of olefins. More specifically, the invention relates to a new method for the preparation of 4-methyl-1-pentene.
The compound 4-methyl-1-pentene is useful as a monomer or as a comonomer in the production of polyolefins. Typically, 4-methyl-1-pentene is produced via the catalytic dimerization of propylene. Commonly employed catalysts include those containing alkali metals or nickel. Low-selectivity catalysts include thorium nitrate, WCl.sub.6, titanium, aluminum alkyls, such as cerium acetylacetonate/aluminum alkyls and certain mixtures of these. Alkali metal catalysts are numerous, but are disadvantageous in that they require high operating temperatures and pressures. Catalysts previously employed for the preparation of 4-methyl-1-pentene via propylene dimerization are all unsatisfactory to the extent that they are not as selective as would be desired. While selectivities to 4-methyl-1-pentene of up to 93 percent have been reported (Chemical Abstracts, 100:102722n, using a Na/K-based catalyst), even this is unsatisfactory in view of the difficulty and expense involved in separating 4-methyl-1-pentene from the commonly coproduced C.sub.6 olefin and C.sub.6 alkane by-products.
U.S. Pat. No. 3,994,945 discloses uranium (IV) tetraallyl compounds and certain halide derivatives thereof. The halide compounds are reported to be useful as catalysts in the stereospecific polymerization of diolefins.
U.S. Pat. No. 3,816,372 discloses uranium (IV) complexes containing metal carbonium .sigma. bonds. Ligands such as allyl, cyclobutadienyl and cyclopentadienyl are taught to be coordinated to the metal by .pi. bonds. The compounds are disclosed as being useful in the oligomerization of olefins and diolefins, and in the insertion reaction of neutral molecules such as CO and NO.
U.S. Pat. Nos. 3,655,811 and 3,808,150 disclose catalyst compositions consisting essentially of (a) an actinide series metal compound such as thorium nitrate tetrahydrate; (b) a reducing agent; (c) a non-protonic Lewis acid; and as optional, preferred ingredients; (d) a trihydrocarbylphosphine; and (e) an inert, organic solvent. The catalyst composition is disclosed as being useful for catalyzing the polymerization of olefins or phenyl-substituted olefins to normally liquid polymers or oligomers, such as catalyzing the dimerization of propylene. Table II in each of said patents indicates that the catalyst compositions are not selective to 4-methyl-1-pentene.
In view of the deficiencies of prior art methods, it would be desirable to have a process which would provide improved selectivity to 4-methyl-1-pentene.